The methyl ester of .alpha.-eleostearic acid (methyl Z, E, E-9, 11, 13-octadecatrieneoate) has been identified as an effective anti feedant for deterring boll weevils from destroying growing cotton. While various methods have been suggested for producing the acid and its ester, these methods are generally of the laboratory variety and expensive to conduct in large scale. In one method for the production of .alpha.-eleostearic acid, which is reported in J. Chem. Soc. (1957) pp. 1632-1646 at 1641, tung oil is saponified and then acidified. The acidified material is washed twice with hot distilled water. After one hour at 0.degree. C., the solid is filtered off and recrystallized four times with ethanol and twice from pentane. The yield of acid is only about 36% based on the weight of the tung oil. In another method. which is described in Jacobson, U.S. patent application Ser. No. 140,911 filed Apr. 16, 1980, tung oil is mixed with ethanol and potassium hydroxide and refluxed for four hours under nitrogen atmosphere. After cooling in an ice bath, a 10% aqueous sulfuric acid solution is added in an amount sufficient to render the system acidic, with the .alpha.-eleostearic acid being present in an oily layer on top of an aqueous layer. Ether, in an amount approximately equal to the volume of the oily layer, is added to the system and the vessel is shaken to dissolve the oily acid in the ether. The ether layer which settles out is then separated and dried with sodium sulfate. The ether is evaporated and the acid residue is taken up in acetone and crystallized out by cooling to about 20.degree. C. The crystals are .alpha.-eleostearic acid, melting point 48.degree. C., and the yield from 134 grams of tung oil is 75 grams of acid. The acid is then esterified with methanol to produce the methyl ester.
While both of the foregoing processes produce good quality product in substantial quantity, it is envisaged that the successful application of the material as a boll weevil anti-feedant for cotton crops will require the much more efficient production of the product than is possible with either of the reported processes.
It is an object of the present invention to provide a new method of producing the methyl ester of .alpha.-eleostearic acid. It is a further object to provide such a process which is simple and inexpensive to operate in large scale. It is a further object to provide such a process in which the product is obtained in high yield.